A number of systems employ one or motors to controllably position an object along a translation axis. One type of system that is of particular interest is an optical system that linearly translates a lens or a lens assembly. The movement of the lens or lens assembly is performed, by example, in order to change a depth of focus. An imaging system having a zoom lens component is one example.
A problem that is inherent in such systems relates to the ability to accurately determine the position of the lens or lens assembly along the linear translation axis. A related problem is in providing an accurate position sensor in a cost effect and simple (both electrically and mechanically) manner.
A number of known types of position sensors can be employed. These known types of position sensors include: (1) an absolute Gray encoder having a digital output; (2) a laser-based time-reflectometer; (3) a laser-based dual beam interferometer; (4) an ultrasonic position sensor; and (5) a linear potentiometer.
However, each of these known types of position sensors has one or more drawbacks. These drawbacks include high cost, high complexity, high power consumption, low resolution, the introduction of friction, and limited lifetime. For example, position sensors that rely on a moving mechanical component, such as a linear potentiometer, are subject to eventual failure. Those position sensors that employ a coherent radiation source (the laser-based systems) are generally expensive to procure, operate, and maintain, and may also require periodic calibration. An ultrasonic sensor will generally not have an accuracy that this sufficient to precisely position an object.
As can be appreciated, for certain applications, such as systems that are intended to be operated on a satellite platform, the position sensor would ideally have a high accuracy, a low power consumption, a long operational life, and would not require periodic maintenance or calibration.